Hot rolling mill lubrication apparatus and process

ABSTRACT

A method and apparatus for applying hot rolling mill lubricants composed of water and difficulty dispersible oil to the rolls of rolling stands used to reduce hot steel whereby the lubricant is applied only during the period when the workpiece contacts the rolls of the rolling stands. The oil is continuously circulated in a loop system to maintain it at a desired temperature range, and then admixed with water when a rolling stand calls for lubrication. Water is preferably continuously fed to the rolls for cooling.

United States Patent [191 Larsonneor 1 Jan. 9, 1973 [54] HOT ROLLING MILL LUBRICATION APPARATUS AND PROCESS [75] Inventor: Louis C. Larsonneor, Palos Heights,

Ill.

[73] Assignee: Nalco Chemical Company, Chicago,

Ill.

[22] Filed: Jan. 4, 1971 [21] Appl. No.: 103,641

Related 0.8. Application Data [63] Continuation-impart of Ser. No. 817,377, April 18,

1969, abandoned.

[52] US. Cl. ..72/21, 72/43, 72/201, 72/236 [51] Int. Cl.....B2lb 37/00, B2lb 27/10, B2lb 45/02 [58] Field of Search ..72/13, 42, 43, 44, 45, 200, 72/201, 202, 236, 21

[56] References Cited UNITED STATES PATENTS 2,310,563 2/1943 Wilke et al. ..72/42 3,150,548 9/1964 Roberts ..72/43 3,208,253 9/1965 Roberts ....72/43 3,605,473 9/1971 Lyon et al. ..72/201 Primary Examiner-Charles W. Lanham Assistant Examiner-E. M. Combs Attorney-Kinzer, Dorn & Zickert, John G. Premo, Charles W. Connors and Edward A. Ptacek 5 71 ABsTRAor A method and apparatus for applying hot rolling mill lubricants composed of water and difficulty dispersible oil to the rolls of rolling stands used to reduce hot steel whereby the lubricant is applied only during the period when the workpiece contacts the rolls of the rolling stands. The oil is continuously circulated in a loop system to maintain it at a desired temperature range, and then admixed with water when a rolling stand calls for lubrication. Water is preferably continuously fed to the rolls for cooling.

9 Claims, 7 Drawing Figures PATENTEDJAN 9 ms SHEET 1 [IF 2 Inventor PATENTEDJAH 9 I973 SHEET 2 [1F 2 Inventor Louis C.Larsonneur HOT ROLLING MILL LUBRICATION APPARATUS AND PROCESS This application is a continuation-in-part of my application Ser. No. 817,377, filed Apr. 18, 1969, now abandoned.

The invention is directed to a method and apparatus for applying hot rolling mill lubricants, which are composed of water and oil, to the rolls of at least one rolling stand whereby the lubricant is applied only during the period when the workpiece contacts the rolls of the rolling stand.

The purpose of using hot rolling mill lubricants is to effectuate a number of the benefits which can only be achieved by the use of lubricants. Effective lubrication during the hot rolling of metals materially increases roll life, thereby reducing the number of roll changes and mill downtime. This results in increased production at lower costs. Proper lubrication minimizes metal pickup from the workpiece and peeling or removal of metal from the-rolls to the workpiece as it goes through the various stands of the rolling operation. Most importantly, proper lubrication during the hot rolling of metal gives an improved product surface quality due to the improved surface condition of the work rolls. In many instances a reduction of roll grinding requirements is also achieved.

The most desirable type of hot rolling mill lubricants comprise a mixture of a lubricating oil or liquid and water which do not easily form an emulsion, and which preferably form a dispersion. Such lubricants are difficult to apply in hot rolling operations whereby oil is preferentially coated on the rolls without being washed from the surfaces by the excesses of aqueous cooling fluids used therewithf Greater benefits would be achieved if such water dispersions could be maintained in a state of uniformity during application to the rolls and then break, whereby the oil was preferentially adsorbed on the rolls. Such-dispersions would not require the useof emulsifiers, thereby allowing used oil simply to be removed and collected from the mill cooling water effluent without necessitating complicated oil and water separation techniques.

If it were possible to produce dispersions by a simple mechanical means whereby such dispersions when formed would be sufficiently stable that they could be fed directly from such mechanical means to the stand of hot metal rolling mills, a flexibility would be afforded to the metal rolling industry. Such would allow the use of a wide variety of lubricant compositions heretofore unavailable due to the difficulty of forming good dispersion.

Such dispersions should be of simple construction and be relatively compact to allow transportation and positioning thereof at advantageous points near the rolling mills where they would be used. Also, such devices should possess sufficient flexibility in design and construction whereby the ratio of oil to water used in various hot rolling mill oil dispersion could be varied by simple means so that such variations could be made by unskilled operators who normally attend such equipment.

Another advantage which would be of benefit to the hot metal rolling art would be a device of a type described which would apply lubricant to a metal workpiece contacting the various stands of a hot rolling mill only at the time that the various rolls of the stand were contacting the workpiece. After the workpiece had been processed by such rolls the supply of lubricant would be discontinued, thereby effectuating a substantial reduction in the quantity of lubricant being used.

The method of the invention includes the steps of continuously circulating oil through a loop system, a part of which would include a heater for cold climates to maintain the oil at a workable temperature, removing from the loop system a quantity of oil in response to a workpiece being in or about to contact a rolling stand, feeding the oil removed from the loop system under pressure to a common lubricant supply conduit, feeding a quantity of water to the common lubricant supply conduit at the desired pressure to mix with the oil. The water is preferably fed continuously to the rolls even when no workpiece is present to effect cooling, while oil is injected into the water on demand ofa lubricant. Suitable apparatus is provided to carry out the method.

It is therefore an object of the invention to provide an improved apparatus and method useful for applying water and oil dispersions to the stands used in the hot rolling of various metals.

Another object of the invention is to provide a method for applying hot rolling mill lubricants composed of water and difficulty dispersible oil to the rolls of rolling stands whereby the lubricant is applied only during the period when the workpiece contacts the rolls and is stopped after the workpiece is no longer in contact with such rolls.

Another object is to provide a method for applying lubricant used in the hot rolling of ferrous metals whereby an oil and water dispersion forming a lubricant is provided which dispersion is formed mechanically.

A further object of the invention resides in the provision of a hot rolling millapparatus for applying a water and oil lubricant on demand in response to the presence of a workpiece wherein the oil is mixed with the water, and where an oil recirculation loop is provided to maintain the oil at a workable temperature.

A still further object of the invention is in the provision of a method and apparatus for applying lubricant to hot rolling mill stands, wherein the lubricant comprises a mixture of water and a difficultly dispersible oil delivered to the rolls through spray headers, and wherein the water is continuously delivered through the headers while the oil is injected in the water during reduction ofa workpiece.

Other objects, features and advantages of the invention will be apparent from the following detailed disclosure, taken in conjunction with the accompanying sheets of drawings, wherein like reference numerals refer to like parts, in which:

FIG. 1 is a schematic view of one form of the apparatus used in practicing the invention;

FIG. 2 shows a lubricant formed by the apparatus as shown in FIG. 1 being applied to two stands of a conventional hot strip rolling mill;

FIG. 3 is a cut-away view showing one form of a mixing orifice used to produce an oil and water dispersion;

FIG. 4 is a schematic view of a modified apparatus according to the invention; FIG. 5 is a schematic view of a further modification;

FIG. 6 is a schematic view of a modified valve arrangement; and V FIG. 7 is a perspective view ofa mixing orifice.

With specific reference to the drawings and, in particular, reference to FIG. 1, there is provided a sensing head 10 which is capable of detecting heat generated by a hot workpiece entering a hot rolling operation by means of infrared impulses emanating from such a hot workpiece. Other types of sensing means may be provided, such as a load cell. The sensing head 10 is connected by electrical lines 12 to a control unit 14 which amplifies the signalfrom the sensing head 10. The amplified signal is delayed to the solenoid valve 116 by the time delay switch 18 which is connected to the control unit 14 through electrical line 16. However, a time delay is optional and not always desired. Also actuated by the. amplified signal ofcontrol unit 14 is a three-way solenoid valve 26 which is connected to the control uriit 14 by means of electrical line 28, and solenoid valves 96 and 118 through electrical lines 98 and 122, respectively. Time. delay switch 18 later activates solenoid valve 116 through line 119.

Pump 24 has its suction or input side 30 connected to oil supply line 32 which is connected to an oil supply, such as a storage tank or reservoir, not shown. Oil supply line 32 is fitted with a Y-shaped T 34 and a strainer 36.

The pump discharge port 38 is connected through a line 40 to the inlet port of three-way solenoid valve 26. One outlet. port of the three-way solenoid valve 26'is connectedto an oil feed supply line 42, and the other outlet port is connected through recirculating line 44 to a T 46, which, in turn, through line 48 connects to the Y-shaped T 34 of oil supply line 32.

It is nowevident that lines 40, 44, 48 and 32 define a recirculating loop system whose operation will be more fully explained hereinafter.

Oil passing through oil'fe'ed supply line 42 is directed to a four-way T 50 whose top is fitted with a pressure gauge 52. L-ine;54 which emanates from the left side of four-way T 50 may be considered as an extension of oil feed supply line 42 and is fitted with three connected Ts 56, 58 and 60. The. left-hand end of T 60 is fitted with a shortnipple 62 and a pipe cap 64.

Emanating from the right-hand side of four-way T 50 is line 51 which is fitted with a valve 53 that controls pressure in line54. Line 51 connects into T 46.

Downwardly extending from the three T's 56, 58 and 60are lines 66, 68 and 70 which are fitted with on-off valves 67,69 and 71 respectively, and check valves 72, 74 and 76 respectively. The on-off valves may be manually or power operated, and of any suitable type.

Fitted at-the bottom of check valves 67, 69 and 71 are mixing orificesor other mixing devices 78, 80 and 82 that direct oil into a common lubricant supply conduit which is designated generally by the numeral 84. The details of a mixingorifice of one type is shown in FIG. 3.

Also feeding into common lubricant supply conduit 84 is water supply line 86, which is fitted with on-off valve 88, strainerand pressure regulator 92. A pressure gauge'94 and a solenoid valve 96, the latter of which is connected by electrical line 98 to control unit 14, is also fitted in water line 86. It can beseen that water supply line 86 is connected to common lubricant supply conduit 84, which receives oil from TS 100, 102 and 104.

The mechanically mixed oil and water forming the lubricant pass through common lubricant supply conduit 84 and enter a fine mesh strainer 106 and from there through line 108, where the lubricant enters T 110. The feed of lubricant is divided evenly through lines 112-and 114 respectively. Line 112 is fitted with a solenoid valve 116. Similarly, line 114 is fitted with a similar solenoid valve 118. Solenoid valve 116 is connected'by means of a suitable electrical conductor 119 to the time delay switch 18, while solenoid valve 118 is connected to the control unit 14 by means of line 122.

As shown to best advantage in FIG. 2, lubricant entering lines 114 and 112 are transmitted to manifold or spray head assemblies 120 and 123 respectively, where lubricant is directed to the surfaces of the top and bottom back-up rolls which are designated by the nu-' merals 128 and 130 respectively. The reduction or work rolls are shown by the numerals 132 and 134,

respectively, while the workpiece is designated 138.

A suitable electrical source, is connected to electrical line which connects-to pumpv switch 20 and the control unit. 14. In operation, pump switch 20, connected to the pump through electrical line 22, is turned on and the pump starts to run. The sensing head or other sensing device 10 positioned in or near the stand Check valves 72, 74 and 76 prevent backflow of water should the oil pressure fall below the water pressure. The strainer 36 in line 32 tends to remove fine abrasive particles, such as grit and dirt, which if remained in the oil would tend to score the pump and damage solenoids and mixing orifices or other mixing devices. When a workpiece nears'the sensing head sighting position, the control unit 14 actuates the solenoid valve 26 which closes to prevent oil flow through line 44, thereby raising the pressure in line 42 and line 54 above the water pressure to cause injection of oil into the line 84. Simultaneously, the valve 96 opens to allow water flow into line 84, and the valve 118 opens to allow lubricant flow into line 114. The valve 116 opens following timing out of time delay 18 which is triggered from control 14 at the same time valves 26, 96 and 116 are actuated.

The amount of oil that is allowed to flow from T 50 into oil feed supply line 54 is=regulated .by means of valve 53 which controls the pressure in feed supply line 54. Oil that is not passed through line 54 because of the by-passing action of valve 53 is returned through line 51 by way ofT 46 into line 48 to line 32 or to tank and is continuously recirculated through the pump.

Oil passing through line 54 is diverted by means of T's 56, 58 and 60, and is further regulated with respect to its flow by means of on-off control or similar valves 67, 69 and 71. The oil leaving these valves passes through mixing orifices 78, 80 and 82, which are shown to best advantage in FIG. 3, where the oil is sprayed under pressure into T's I00, 102 and 104 and thereby enter common lubricant supply conduit 84 to mix with the water stream.

As oil passes through common lubricant supply conduit 84, water at a regulated pressure, if necessary, is also passing into this same line through line 86 which is connected to line 84. Water supply line 86 is fitted with an on-off valve 88, and optionally a strainer 90 which acts to remove foreign particles from the water. To insure uniformity of pressure within the common lubricant supply conduit, water supply line 86 is fitted with pressure-regulating valve 92, which allows water at a substantially constant pressure to enter line 84. Line 86 is fitted with solenoid valve 96, which is actuated in response to the energizing of sensing head through means of control unit 14.

When water passing through water supply line 86 enters common lubricant supply conduit 84, it contacts the oil sprays produced by mixing orifices 78, 80 and 82 where a thorough and intimate mixture of the oil occurs by forming a relatively short-lived yet stable dispersion.

As the oil dispersed in line 84 contacts strainer 106, which contains finely-spaced filter media (e.g., 50 mesh or less, most typically 100 mesh) it is further filtered where it is then fed through T 110 into lubricant feed lines 114 and 1 12. The strainer 106 is optional and needed only when the openings in the spray headers might be clogged by particles that may pass through the initial strainers in the oil and water line. Time delays are only used where necessary and are applicable to stands receiving the workpiece from the first stand, and even where plural stands are employed time delays may not be needed. As the lubricant leaves lines 114 and 112, it is transmitted to spray heads 120 and 123, where it contacts the delivery side of the top and bottom back-up rolls 128 and 130, which thereby supplies lubricant to all the rolls and the workpiece 138.

As the workpiece passes beyond the sensitivity limitations of the sensing head 10, the sensing head deenergized by means of the control unit 14 the solenoid valves 96, 116 and 118 which are returned to the closed position. Actuation of the three-way solenoid 26 in response to the deenergizing of sensing head 10 opens recirculating line 44 to drop the pressure in lines 42 and 54, and oil recirculates throughout the recirculating loop previously described.

It is understood that the time delay switches are set to correspond to the normal speed of the workpiece through the rolling stands. Thus, when the infrared sensing head energizes the control unit, the lubricant will be applied to the rolls of each stand just as the workpiece enters it and for a period of time sufficient to allow the workpiece to pass therethrough.

It will be further understood that numerous variations and adaptations of the invention may be made by those skilled in the art without departing from the spirit thereof.

In actual mill practice, the apparatus of the invention will be so constructed to supply lubricant to several of the stands used in a metal reduction operation. Thus, for example, good results may be achieved if spray illustrated by numerals 120 and 123 are placed at, for instance, the second, third, and last stands. The number of rolls treated and the sides treated can, of course, be-

varied infinitely by increasing the number of lines corresponding to lubricant supply lines 112 and 114 respectively.

The pressure regulating valve, solenoid valves, and the like, allow control of pressure and feed of the oil and water components of the finished lubricant. Typical of the dispersions that can be produced are dispersions which contain from 0.001-50 percent of a lubricating oil with the balance being water. In actual use, it has been found that the invention allows the elimination of substantially all of the emulsifiers normally used to prepare a hot mill rolling emulsion-type lubricant, and yet the dispersed lubricant applied by the device is completely uniform and stable through application. It allows excellent lubrication to be afforded.

While the apparatus and methods described are directed to producing uniform dispersions of oil and water for use in the hot rolling of metal, it is understood these same techniques and apparatus may be used for some stable emulsions of oil and water in the presence of emulsifying agents.

From the foregoing, it will be understood that the apparatus disclosed in FIGS. 1-3 operates to apply a lubricant composed of water and oil to the roll stands upon demand when a workpiece is moving through the roll stands, and when no workpiece is moving through the roll stands, the lubricant is discontinued. A variation and preferred arrangement is illustrated in FIG. 4, wherein water is continually supplied to the spray headers adjacent the roll stands and oil is injected into the water to form a lubricant upon demand during the presence of a workpiece. Thus, the rolls in a stand are being cooled by the continuous application of water thereto in the absence of a workpiece from the same spray headers that produce'the lubricant when needed. As in the embodiment of FIGS. 1-3, the lubricant comprises a dispersion of oil and water wherein the oil is mechanically mixed with the water by being injected into the water with a suitable mixing device.

Referring to FIG. 4, the apparatus there illustrated for applying cooling water and lubricant to a roll stand operates to apply the lubricant during the presence of a workpiece and to apply cooling water during the absence of a workpiece. Roll stand 145 includes work or reducing rolls 146 defining a bite through which a workpiece 147 moves, and back-up rolls 148. This roll stand is only exemplary of one type of roll stand to which the present invention may apply, and it is understood that the present invention may be used in conjunction with any type of roll stand, whether it have two, three or four rolls, and to a plurality of roll stands arranged in a group, if that be desired. Spray headers 149 apply the cooling water or lubricant to the delivery side of the back-up rolls 148. It should be recognized that the spray headers may be arranged to apply the lubricant and/or cooling water directly to the work rolls if desired, and in that case such could be applied at the entry side.

A common line 150 connecting to the spray headers 149 is connected to a cooling water and/or lubricant line 151 through a T 152, so that whatever is passing through the line 151 is substantially equally distributed between the spray headers 149. The line 151 is connected to a I 153 which is connected to a water supply line 154 and an oil injection line 155. The water supply line 154 continually supplies water to the line 151 at a relatively constant pressure, and when the oil pressure in line 155 exceeds that of the water pressure, oil is injected into the water to form the lubricant dispersion which is then delivered to the spray headers 149. A mixin'g device 156 in the form of a mixing orifice eductor, or other suitable structure, functionsto mix the oil into the water at the T 153 when the oil pressure in line 155 exceeds that of the water pressure in line 154.

In order to prevent b ack flow of water into the oil line 155, a check valve 157 is provided. A conventional on-off valve 158 is provided in line 155 ahead of the check valve 157.

The oil injection line 155 is connected through a T 159 to port, 160 of a three-way solenoid valve 161, and to a recirculating pressure control or return line 162. The solenoid valve 161 includes an inlet port 163 connected to the discharge 164 of pump 165 by a line 166. A second outlet port 167 of the solenoid valve 161 is connected through, a T 168 to the suction 169 of the pump 165 through'a recirculating line 170; A pressure regulating valve 171 is provided in the line 170 to maintain maximum oil flow through return line 162 without injection of oil into the water stream when the solenoid valve .161 is open to allow oil flow through both outlet ports 160 and 167.

A pressure regulating valve '172 is provided in the return line 162 and is set to cause the oil pressure in line 155 to exceed that of the water pressure to cause injection of oil into the water stream when the solenoid valve .161 is closed and .oil discharge is only permitted through outlet portion 160. The return line 162, since the valve 172 is always at least cracked, recirculates oil into the oil storage tank or reservoir 173. Oil is drawn from the tank 173 through line 174 to the suction side of the pump through T 168. A strainer 175 is provided in the line 174 to filter out particles that would impede operational oil flow and/or damage elements in the circuit.

During normal operation of the roll stand 145, in the absence of a workpiece water is supplied to the spray headerv 149 to effect a cooling action on the rolls. The pump l65xwould be continually running and would be recirculating oil through recirculating line 170 and return line 162. A heater 176 maintains a substantially constant temperature of, the oil in the tank 173, and recirculation maintains the oil in the lines at. a working temperature. During this stage of operation, the solenoid valve 161 is open to allow discharge from both outlets ports 160 .and 167. Upon the detection of a workpiece at or near the roll stand 145 by the detector 177, a signal is transmitted to a control unit 178 operating the solenoid valve 161 to close off the outlet port 167 thereby increasing the oil pressure in injection line 155 above the pressure of .water in the water line 154 to cause injection of oiliinto the water and the formation ofa lubricant dispersion for application to the rolls. The water in the lubricant dispersion cools the rolls, while the oillubricates. Thereafter, when the detector no longer sees the presence of a workpiece, the signal will be removed from the control unit 178 to allow the solenoid valve 161 to open so that oil will be discharged from bothoutletports of the valve thereby decreasing the pressure in the injection line 155 below that of the water pressure and ceasing injection of oil into the water. Only waterwill then be discharged from the spray headers 149 to effect a continuing cooling action on the rolls. When the solenoid valve 161 is opened, oil

is recirculated through the line 170 and the return line 162, anclupon closure of the valve 161, oil is recirculated only through return line 162. Accordingly, the temperature of the oil 'will be maintained at a working level by the recirculation. Further, oilwill be injected into the water stream to form a lubricant only when a lubricant is needed during the presence of a workpiece at the roll stand.

it will be recognized that any number of spray headers may be provided for one or more roll stands depending upon the installation, and selective oil injection into the water stream for any one roll stand may be accomplished by suitable instrumentation and controls. While any type of mixing device 156 may be provided, one form is shown in FIG. 7, which is of the mixing orifice type, wherein an orifice 179 is provided through which the oil is forced under, pressure from the oil injection line into the water stream of the common line for mechanical mixing therewith. Depending upon the installation, pressure in the oil injection line and the size of the orifice 179 will be coordinated to define the proper mixing operation.v

The solenoid valve 161 may be defined as a threeway valve in that it includes one inlet port and maybe conditioned to discharged through one or both of the outlet ports, but it should be understood that any suitable valve arrangement may be provided to accomplish the split and/or single stream flow. To illustrate another form, reference is made to FIG. 6, wherein like reference numerals are applied to like elements for purposes of clarity, it being here shown that the pump discharge line 166 is connected to a T 180, which in turn splits the stream to oil injection line and recirculating line 170. A simple on-off two-way solenoid valve 181 is provided in the recirculating line'170 to stop or allow oil flow through the recirculating line and control oil pressure in the oil injection line 155.

The embodiment of FIGS differs from the embodiment of FIG. 4 only in that the recirculating line is connected directly to the oil tank 173, this arrangement providing better circulation through the heated body of oil in the tank 173. Otherwise, the arrangement 7 of this embodiment operates in the same fashion as that of FIG. 4.

it will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of the present invention, but it is understood that this application is to be limited only by the scope of the appended claims,

This invention is hereby claimed as follows:

1. Apparatus for applying a hot rolling mill lubricant of water and a difficultlydispersible oil to a roll stand during the presence of a workpiece in the stand, said apparatus comprising sprayheader means at the roll stand from which the lubricant is discharged onto the roll stand during the presence of a vworkpiece, a common lubricant water line connected to said spray header means, a pressurized water supply connected to said common line to continuously provide water thereto at a given pressure range, means for injecting oil into the common line to mix with the water and form a lubricant dispersion, said injection means including an oil injection line connected into the common line, a pump having a suction port and a discharge port, an oil supply connected to the suction port, an oil recirculating line connected on one side to said supply, a discharge line connected from the pump discharge port to the other side of the oil recirculating line and to the oil injection line, and valve means between the discharge line, the oil injection line, and the oil recirculating line for selectively closing communication between the discharge line and the recirculating line to raise the pressure in the oil injection line above the water pressure in said common line and cause injection of oil into the water.

2. Apparatus as defined in claim 1, which further includes a return line between said oil injection line and said supply, and a pressure regulating valve in said return line set so that the oil pressure in the oil injection line when said valve means is closed exceeds the water pressure.

3. Apparatus as defined in claim 2, which further includes a pressure regulating valve in said oil recirculating line set to maintain maximum flow through said return line when the valve means is open without causing injection of oil into the water.

4. Apparatus as defined in claim 3, which further includes means detecting the presence and absence of a workpiece at the roll stand for controlling said valve means to cause injection of oil into the common line during the presence of a workpiece.

5. Apparatus as defined in claim 4, which further includes means for heating the oil supply.

6. Apparatus for applying a hot rolling mill lubricant of water and difficulty dispersible oil to a roll stand during the presence of a workpiece in the stand, said apparatus comprising spray header means at the roll stand from which lubricant is discharged onto the roll stand during the presence of a workpiece and from which water is discharged onto the stand during the absence of a workpiece, a common lubricant-water line connected to said spray header means, a pressurized water supply connected to said common line to continuously provide water thereto, means for injecting oil into the common line to mix with the water and form a lubricant dispersion, said injection means including a continuously operating pump having a suction port and a discharge port, an oil injection line between said pump discharge port and said common line, an oil supply, an oil supply line connected between the oil supply and the pump suction port, a recirculating line between the suction and discharge ports, an oil injection control valve means in the recirculating line and connected to the oil injection line for selectively stopping oil flow in the recirculating line and causing the injection of oil through the oil injection line into the common line, a mixing device in the oil injection line at the common line to cause mixing of the oil into the water during oil injection, check valve means in the oil injection line upstream of the mixing device preventing backflow of water through the oil injection line, an oil return line connecting between the oil supply and the oil injection line upstream from said check valve means, a pressure regulating valve in said return line set so the oil pressure in the oil injection line exceeds the water pressure in the common line when said oil injection control valve means is closed to then cause oil injection into the common line while bleeding oil back to said oil supply, wherein the oil pressure in the oil injection line is less than the water pressure in the common line when the or] injection control valve means 18 open and oil is being recirculated in both the oil recirculation line and the return line.

7. Apparatus as defined in claim 6, wherein said oil injecting means further includes means for heating the oil supply.

8. Apparatus as defined in claim 6, wherein said oil injecting means further includes a pressure regulating valve in said oil recirculating line set to maintain maximum flow through said return line when the oil injection control valve means is open without causing injection of oil into the water.

9. Apparatus as defined in claim 8, which further includes means detecting the presence and absence of a workpiece at the roll stand for controlling said oil injection valve means to cause injection of oil into the common line only during the presence of a workpiece. 

1. Apparatus for applying a hot rolling mill lubricant of water and a difficultly dispersible oil to a roll stand during the presence of a workpiece in the stand, said apparatus comprising spray header means at the roll stand from which the lubricant is discharged onto the roll stand during the presence of a workpiece, a common lubricant water line connected to said spray header means, a pressurized water supply connected to saId common line to continuously provide water thereto at a given pressure range, means for injecting oil into the common line to mix with the water and form a lubricant dispersion, said injection means including an oil injection line connected into the common line, a pump having a suction port and a discharge port, an oil supply connected to the suction port, an oil recirculating line connected on one side to said supply, a discharge line connected from the pump discharge port to the other side of the oil recirculating line and to the oil injection line, and valve means between the discharge line, the oil injection line, and the oil recirculating line for selectively closing communication between the discharge line and the recirculating line to raise the pressure in the oil injection line above the water pressure in said common line and cause injection of oil into the water.
 2. Apparatus as defined in claim 1, which further includes a return line between said oil injection line and said supply, and a pressure regulating valve in said return line set so that the oil pressure in the oil injection line when said valve means is closed exceeds the water pressure.
 3. Apparatus as defined in claim 2, which further includes a pressure regulating valve in said oil recirculating line set to maintain maximum flow through said return line when the valve means is open without causing injection of oil into the water.
 4. Apparatus as defined in claim 3, which further includes means detecting the presence and absence of a workpiece at the roll stand for controlling said valve means to cause injection of oil into the common line during the presence of a workpiece.
 5. Apparatus as defined in claim 4, which further includes means for heating the oil supply.
 6. Apparatus for applying a hot rolling mill lubricant of water and difficulty dispersible oil to a roll stand during the presence of a workpiece in the stand, said apparatus comprising spray header means at the roll stand from which lubricant is discharged onto the roll stand during the presence of a workpiece and from which water is discharged onto the stand during the absence of a workpiece, a common lubricant-water line connected to said spray header means, a pressurized water supply connected to said common line to continuously provide water thereto, means for injecting oil into the common line to mix with the water and form a lubricant dispersion, said injection means including a continuously operating pump having a suction port and a discharge port, an oil injection line between said pump discharge port and said common line, an oil supply, an oil supply line connected between the oil supply and the pump suction port, a recirculating line between the suction and discharge ports, an oil injection control valve means in the recirculating line and connected to the oil injection line for selectively stopping oil flow in the recirculating line and causing the injection of oil through the oil injection line into the common line, a mixing device in the oil injection line at the common line to cause mixing of the oil into the water during oil injection, check valve means in the oil injection line upstream of the mixing device preventing backflow of water through the oil injection line, an oil return line connecting between the oil supply and the oil injection line upstream from said check valve means, a pressure regulating valve in said return line set so the oil pressure in the oil injection line exceeds the water pressure in the common line when said oil injection control valve means is closed to then cause oil injection into the common line while bleeding oil back to said oil supply, wherein the oil pressure in the oil injection line is less than the water pressure in the common line when the oil injection control valve means is open and oil is being recirculated in both the oil recirculation line and the return line.
 7. Apparatus as defined in claim 6, wherein said oil injecting means further includes means for heating thE oil supply.
 8. Apparatus as defined in claim 6, wherein said oil injecting means further includes a pressure regulating valve in said oil recirculating line set to maintain maximum flow through said return line when the oil injection control valve means is open without causing injection of oil into the water.
 9. Apparatus as defined in claim 8, which further includes means detecting the presence and absence of a workpiece at the roll stand for controlling said oil injection valve means to cause injection of oil into the common line only during the presence of a workpiece. 